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Henry L. Ellsworth, U. S., Commissioner of Patents, said in 1844:
"...The advancement of the arts from year to year taxes our credulity and seems to presage the arrival of that period when further improvements must end."

Source: Woods, Ralph L. Prophets Can be Right and Prophets Can be Wrong. American Legion Magazine, October 1966. p. 29

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Proposal to apply steam power to ships (early 1800's.): Sir Joseph Banks, English explorer-naturalist and President of the British Royal Society, said:
"...a pretty plan; but there is just one point overlooked -- that the steam engine requires a firm basis on which to work!"

Proposal to drive a steamboat by screw-propeller: Sir William Symonds, Surveyor of the British Navy, commented in 1837:
"...even if the propeller had the power of propelling a vessel, it would be found altogether useless in practice, because the power being applied in the stern it would be absolutely impossible to make the vessel steer."

Source: Church, William Conant. The Life of John Ericsson, New York, Charles Scribner's Sons, 1890. p. 90.

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Lee de Forest:
In 1913 Lee de Forest, inventor of the audion tube, which device makes radio broadcasting possible, was brought to trial on charges of fraudulently using the U. S. mails to sell the public stock in the Radio Telephone Company, a worthless enterprise. In the court proceedings, the District Attorney charged that:
"De Forest has said in many newspapers and over his signature that it would be possible to transmit human voice across the Atlantic before many years. Based on these absurd and deliberately misleading statements, the misguided public...has been persuaded to purchase stock in his company..."

De Forest was acquitted, but the judge advised him :
"to get a common garden variety of job and stick to it."

Limited utility of radio
W. W. Dean, President of the Dean Telephone Company told Lee de Forest in 1907:
"...You could put in this room [his office], de Forest, all the radiotelephone apparatus that the country will ever need!"

Source: De Forest, Lee. Father of Radio, the Autobiography of Lee de Forest. Chicago, Wilcox and Follett Co., 1950. p. 232.

Friends of Lee de Forest asked:
"Well, then of what possible use can your 'radiotelephone' be? It can't compare with the wire phone, you say, and it can't cover the distances that the wireless telegraph can cover. Then what the hell use is it anyway Lee?"

Source: De Forest Lee. Father of Radio, the Autobiography of Lee de Forest. Chicago, Wilcox and Follett Co., 1950. p. 227.